1. Field of the Invention
The present invention relates in general to assemblies for mounting or coupling the shank of a ground tool to the tool bar of a soil tilling farm implement, and more specifically relates to such assemblies that release the ground tool for pivotal movement out of an operating position upon encountering obstructions in the soil.
2. Description of the Prior Art
Assemblies for movably coupling ground tools to a tool bar of a soil tilling farm implement are well known in the art. A typical such assembly is disclosed in U.S. Pat. No. 2,493,811 wherein a tool has a shank pivotally interconnected to a support plate and to a spring unit that has a coil spring compressed when the tool is pivoted. The coil spring provides an initial pressure on the tool to hold it in a normal operating position during soil tilling operation. When the tool encounters an obstruction in the soil the force applied on the tool overcomes the initial spring pressure and pivots the tool from the normal operating position. When the obstruction has been passed, the compressed spring causes the tool to return to the normal operating position therefor.
The above type of assembly provides an improvement over a fixed mounting of a tool to a tool bar. However, in operation the pressure exerted by the coil spring during pivotal movement of the tool to the obstruction passing position therefor is progressively increased. U.S. Pat. No. 3,700,039 discloses an assembly intended to reduce this problem by decreasing the moment arm of the spring force, as the spring is compressed, so that the counter force required to pivot the tool is maintained only slightly greater than the initial tool holding force. However, neither of the above references provides an assembly that holds a tool in an operating position with a force that is substantially decreased as the tool is pivoted out of the operating position to minimize tool damage as the result of encountering an obstruction.